The present invention relates to processes for the vacuum treatment of workpieces as well as to corresponding process.
A group of several workpieces is subsequently referred to as xe2x80x9cbatchxe2x80x9d.
The simultaneous vacuum treatment of entire batches has been known for a long time. The traditional procedure was to load a vacuum chamber with a batch, to pump down the vacuum chamber and to treat the batch inside the vacuum chamber. After the treatment process the vacuum chamber was vented, opened and the treated batch removed.
This procedure is limited to processes in which a batch treatment can be performed consecutively, usually with intermediate phases in normal atmosphere. This means that such a batch treatment is not feasible for workpieces that require a series of vacuum treatment steps, all or most of which must fulfill demanding cleanliness requirements. For this type of critical process sequences a different treatment technique has been developed in which the workpieces are loaded through a vacuum lock and, without leaving the latter, are subjected to a series of treatment process steps such as coating processes in all known vacuum engineering versions including CVD, LPCVD, PECVD, PVD, as well as etching processes, cleaning processes, heating or cooling processes.
From U.S. Pat. No. 5,344,542, for example, a known solution is to submit workpieces from a load lock hopper station via a centrally arranged vacuum transport chamber to several connected treatment stations for which purpose a transport robot is used in the transport chamber. To minimize cross-contamination between the individual treatment steps in the treatment stations through the transport chamber, the treatment stations can be vacuum isolated relative to the transport chamber by means of valves. The workpieces are transported individually to the desired process stations via the transport chamber.
If different types of treatment stations that satisfy specific requirements are flanged to such a transport chamber this also results in different requirements with respect to the time sequence based on which the individual workpieces must travel through the individual treatment stations, and also with respect to the treatment time to which the individual workpieces are subjected at the corresponding treatment stations. To achieve flexibility in subjecting the individual workpieces to the intended treatment, U.S. Pat. No. 5,344,542 also proposes to make the robot arrangement interact with a process controller at which the required time sequence based on which the treatment stations are served by the robot arrangement can be freely defined.
Also known from U.S. Pat. No. 5,019,233 is the application of the single workpiece treatment principle to highly complex and critical workpiece treatments under vacuum condition, and in particular to treatment steps that are highly sensitive to contamination as discussed in connection with U.S. Pat. No. 5,344,542. It is acknowledged, however, that the workpieces after they have been loaded into an input lock, must first be conditioned, that is, degassed in such a way that subsequently they do no introduce absorbed external gasses as contamination into the highly critical processes. If according to U.S. Pat. No. 5,019,233 this necessary conditioning of the workpieces is performed when they are loaded through the vacuum lock, relatively long conditioning times are required. The vacuum lock becomes the slowest element of the process sequence and significantly limits the throughput of a corresponding treatment plant.
There the problem is solved in such a way that two load locks are operated in parallel. A workpiece batch is transported into the first load lock where it is conditioned and subsequently transferred into a second vacuum lock. From the latter one workpiece at a time is distributed via the central transport chamber to the appropriate treatment stations, again in a user selectable sequence, while already the next batch is loaded and conditioned in the first vacuum lock. For sequencing the highly delicate process steps in the treatment stations, the aforementioned single workpiece treatment process is still followed. Only for loading through the vacuum lock and for conditioning as well as for unloading the workpieces are grouped into batches.
A similar procedure is followed according to EP 0 608 620. Basically also there the workpieces are to be subjected to a complex sequence of individual, critical vacuum treatment steps. Also in this case the aforementioned concept of loading and unloading the workpieces in batch mode through the vacuum lock and subjecting the workpieces individually to the various treatment steps is still maintained.
According to that patent application thin glass substrates are to be treated. An acute breakage problem is said to exist if such substrates are exposed to abrupt temperature changes. However, if such glass substrates are to be individually heated and cooled gradually in single workpiece treatment mode, the throughput of the overall system is significantly impaired as already mentioned in U.S. Pat. No. 5,019,233. As in the case of U.S. Pat. No. 5,019,233 also here the slowest steps of the process sequence, that is, gradual heating and gradual cooling are still performed in batch mode. Besides, these are process steps that are rather uncritical. Also according to this application a batch of workpieces is loaded through the vacuum lock and the loaded batch is then slowly heated as a batch in a heating station. Subsequently, however, the workpieces are transported individually to the various treatment stations and then collected as a batch in the exit chamber where they are gradually cooled before they are unloaded to atmosphere.
As can be seen, the concept of treating each workpiece requiring a complex sequence of process steps individually, that is, one workpiece at a time, was systematically followed. One of the major reasons for this was also the prevailing opinion that with a complex sequence of process steps and relatively costly workpieces to be treated, only individual workpiece treatment was suitable for achieving adequate control over the processes and for controlling, monitoring and reproducing the process sequence, and in addition to limit the damage to a few workpieces in the event of a process fault.
As far as is known DE-OS 44 12 902 was the first application which proposed that also in such highly delicate workpiece treatment processes the workpieces should not only be loaded and unloaded through vacuum locks in batch mode, but also be submitted as a batch to a central transport chamber, from where they are submitted to and handled as batches in the various treatment stations. For further increasing the throughput, several identical or identically operated treatment stations are operated in parallel.
Under a first aspect the present invention is akin to a process or a system of the last mentioned type. As mentioned above, the workpieces are loaded and unloaded through vacuum locks in batch mode, transported, and submitted in parallel to several identical treatment stations. The objective of the present invention is to give this approach a high degree of adaptation flexibility for different process sequences while preserving the high production rate in said workpiece treatment even in situations where within the framework of the desired flexibility very critical, highly divergent process steps must be implemented in a complex sequence.
When at least one vacuum station is available in which the workpieces are surface treated, that is, coated or eroded in batch mode, this is achieved by means of a process controller through which the timing for feeding and removing the workpieces to and from the corresponding vacuum stations is freely definable.
This breaks with the prevailing opinion that batch processing of workpieces, which is pursued by this invention by means of a definable sequence of treatment steps for highly complex treatment process sequences, cannot be efficiently implemented even with flexibly selectable, difficult process steps.
The process according to the present invention and the corresponding process equipment according to claim 1 and 15 respectively make it possible to selectively configure with the same basic equipment a variety of different batch treatment processes or treatment sequences according to user specifications or even in accordance with the requirements of individual product series. With the same basic batch configuration and despite the resulting high throughput, the configuration flexibility advantages known only for single workpiece treatment systems can be achieved and thus it becomes possible to implement process steps and in particular process step sequences in batch mode which in the past were the exclusive domain of single workpiece treatment.
Given the said application flexibility of one and the same system, a second aspect of the present invention is based on the following insight: If on a treatment system two or more vacuum stations are installed into which the workpieces are loaded as batches in accordance with the aforementioned concept, the situation may occur in which the batch size on one or the other installed vacuum station should be smaller than on another vacuum station, depending on its type and implementation effort.
In this respect reference can be made to U.S. Pat. No. 5,590,994. On the system known from this patent application the first vacuum station in this sense is a transport station featuring a transport carrousel holding the batch of workpieces. Before the workpieces are transferred from the transport carrousel batch to a subsequent transport robot from which they are supplied to the individual treatment stations in single workpiece mode, they are deposited by the former in a large conditioning chamber. There, a much larger workpiece batch is accommodated than in the aforementioned transport chamber. The conditioning chamber is operated cyclically, that is, from said transport chamber a workpiece is inserted into the conditioning chamber while at the same time a previously conditioned workpiece is retrieved. This shows that already in said patent application it was realized that it can be highly advantageous to use batch mode vacuum stations that accommodate batches of different sizes. As mentioned, however, the treatment as well as the transport between the two vacuum stations of different batch size are performed in single workpiece mode.
Under this second aspect the objective of the present system is to modify the process of the aforementioned type in which always at least two vacuum stations for different batch sizes are provided, so that a higher throughput of the overall system is achieved than with the single workpiece transfer and treatment process implemented in the known system. With the process according to claim 2 and the equipment according to claim 16 this is achieved by implementing the transport to and/or from the stations accommodating different batch sizes in batch mode, that is, not as one workpiece at a time to or from said stations but simultaneously with several workpieces, that is, a transport batch.
This preserves the possibility to process different batch sizes, depending on the installed vacuum station type while still systematically following the batch handling principle. In this way, for example, a vacuum station designed as a vacuum lock can be designed for a very large batch and the transport robot removes, quasi as a portion, a smaller batch from the vacuum lock batch and transports it to the corresponding treatment station which should be designed in such a way that not all workpieces of the vacuum lock batch can be treated simultaneously.
As shall be explained later an additional step of the present invention is to vary also the size of each transported batch under process control which in systems with several vacuum stations accommodating different batch sizes gives the possibility to optimize the entire process sequence, that is, as a function of the batch source from which a transport to a specific destination batch must be accomplished. This aspect of the invention occasionally controls also a xe2x80x9cbatch size 1xe2x80x9d and consequently a single work piece.
Under this third aspect the present invention which aims to achieve maximum application flexibility combined with optimum throughput is aware, for example, based on U.S. Pat. No. 5,590,994, that with vacuum stations of different batch sizes at least two vacuum stations with such different batch sizes can be provided for which the loading and/or unloading with one and the same transported batch size is, however, not optimal. For example, if the one vacuum station to be loaded is designed for a batch size of nine and the second one for a batch size of ten, it is obvious that one and the same transport batch size, be it either three or five, is not suited to be used rigidly for both stations. Under this aspect the present invention proposes in accordance with the wording of claim 3 that in a workpiece treatment process comprising at least two vacuum stations in which the workpieces are accommodated as batches, to load or unload these vacuum stations with workpiece batches, the size of which can be controlled. If these two stations are supplied, for example, by the same transport robot, it is proposed, for example, to provide means for the latter through which the number of workpieces to be picked up by the robot can be controlled for each operating cycle.
A system designed according to this aspect is specified in claim 17.
Preferably also here the transport batch size sequence is freely definable by means of a process controller, or optimized by such a controller based on parameters such as station batch sizes and process step sequences.
As mentioned it is feasible to reduce the transport batch size to a single workpiece, if this is required.
Under a fourth aspect of the present invention it is recognized that if one and the same basic equipment configuration is used for building different overall configurations, it should be noted thatxe2x80x94as discussed under the third aspectxe2x80x94vacuum stations can also be designed for different batch sizes. According the wording of claims 4 and 18 it is proposed that the number of workpieces of the station batches shall be freely definable by a process controller. If, for example, a vacuum station with a batch size of ten is installed at one of the work openings of a transport chamber, and on another work opening a vacuum station with a station batch size of five, this can be readily accommodated according to the invention in that the process controller is given information on a case by case basis concerning the station batch size to be expected at the corresponding work opening; the controller can then calculate the optimum transport batch sizes either as fixed or variable quantities.
Other preferred design versions of the present invention under all aspects with respect to the process, contemplates as well as the preferred design version of the equipment.
Preferably at least some of the installed vacuum stations are vacuum isolated from each other, if necessary, in such a way that the possibility of contamination of individual process steps by others is precluded.
The processes according to the invention as well as the corresponding equipment are particularly suitable for treating flat workpiece discs, in particular semiconductor wafers, memory discs, substrates for active displays, basically two-dimensional flat and three-dimensional workpieces, with the latter including, for example, machine components, tools, in particular for metal cutting and shaping, for example, for depositing wear protection coatings.